This invention relates to a caster wheel which minimizes self-excited vibration. More particularly, this invention is directed to a caster wheel operable for safe use with a wheelchair, gurney, cart, and the like.
Caster wheels have been widely utilized in the past for a wide variety of purposes in environments where free steering is desired. Caster wheels are journalled about a vertical thrust bearing and when pointed exactly in the direction of motion of the object there is no driving force for an undesirable, self-excited vibration. If there is any disturbance that causes a deviation of the caster wheel's direction or a transverse acceleration of the frame, however, a self-excited vibration, or shimmy, may begin. Once vibration is initiated, the amplitude will either diminish and cease or it will increase and persist. If caster wheel shimmy is permitted to continue or increase amplitude, it will tend to impede forward motion of the object to which it is journalled, increase the difficulty in steering, and present other control problems. Moreover, shimmy produces substantial forces on the vertical journal such that the physical integrity of the bearing may be jeopardized.
While caster wheel shimmy may be annoying with regard to a shopping cart or the like, shimmy problems can become significantly more critical with regard to caster wheels utilized for wheelchairs, gurneys, carts, and the like. In this connection, if a wheelchair caster is permitted to shimmy in an undamped fashion, more strength and dexterity is required by an operator of the chair. In the event a wheelchair is power driven, more energy is required of the motor assembly. This causes a reduction in battery energy which is already a limitation with powered wheelchairs. Still further, harmonic caster wheel shimmy has the potential of excessively wearing or damaging the frame of a wheelchair. Most significantly, excessive caster wheel shimmy may create a safety hazard in wheelchair or gurney use. In this regard, the onset of drag on a wheelchair due to shimmy of one of the caster wheels has the potential of causing the wheelchair to suddenly turn and even throw the user out of the chair.
In any or all of the above instances, a rider experiences at least some degree of discomfort and in some instances, caster shimmy presents a significant safety hazard.
Although it may be feasible to temporarily eliminate the effect of caster wheel shimmy with a manual wheelchair by reducing the speed of operation, such reduction in speed is quite inconvenient to an operator. With a motor driven unit, speed reduction is not always possible in time to prevent an accident.
The difficulties suggested in the preceding are not intended to be exhaustive but rather are among many which may tend to reduce the effectiveness of prior caster wheels. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that caster wheels appearing in the past will admit to worthwhile improvement.